Interventional catheters having cutter assemblies and differential cutting surfaces for use in such assemblies

ABSTRACT

A rotatable operating head for removal of obstructive material from a target site in a body lumen or cavity is operably connected to a rotatable, translatable drive shaft, that is driven by a drive motor and received through an elongated catheter. The operating head includes a plurality of differential cutting blades, with at least one of the cutting blades being a stepped blade, the stepped blade comprising a raised cutting surface positioned adjacent, or in proximity to, a shoulder region.

REFERENCE TO PRIORITY APPLICATIONS

This application claims priority to U.S. provisional patent applicationNos. 60/894,173 filed Mar. 9, 2007, and 60/828,209 filed Oct. 4, 2006.The disclosures of these priority applications are incorporated byreference herein in their entireties.

FIELD OF THE INVENTION

The present invention relates to methods and systems for removingmaterial, such as obstructions and partial obstructions, from aninternal lumen or cavity of a mammalian subject, such as a blood vessel.More particularly, the present invention relates to interventionalcatheters having rotating operating heads incorporating blade structuresfor removing obstructions and partial obstructions from a lumen orcavity.

BACKGROUND OF THE INVENTION

Removal of disease such as atherosclerotic plaque, thrombus and othertypes of obstructions and partial obstructions from internal body lumensor cavities using advanceable, rotating operating heads is awell-established interventional technique. Numerous interventionalcatheters have been conceived and developed. Most of these systemsrequire placement of a guiding catheter and guide wire prior tointroduction of the interventional catheter and placement of theinterventional catheter at the target operating site. Many of theseprior art systems incorporate mechanical aspiration systems to removefluid and particulates from the site, and some systems incorporate orare used in conjunction with other mechanisms such as distal filters forpreventing removed material from circulating in the blood stream.

Despite the many and varied approaches to material removal systems, manychallenges remain in providing systems for removing material from alumen, such as a blood vessel, safely and reliably and without causingcomplications. The safety and reliability of the system is manifestlycritical. Recovery of debris generated during a material removaloperation, or reducing the size of the debris to a particle size thatwill not produce blood vessel damage or embolic events, is essential.The flexibility and size of an interventional catheter are alsoimportant features. The system must be small enough and flexible enoughto navigate through sometimes tortuous internal structures andpassageways, such as blood vessels, for placement at the targetinterventional site. The interventional catheter must also havesufficient integrity and a combination of stiffness and flexibility tooperate reliably at high rotational rates while allowing for aspirationof fluids from the site and/or infusion of fluids to the site.

In interventional catheters that employ a “cutting head,” any cutterstructures must be benign or retained in a protective sheath duringnavigation of the operating head to and from the interventional targetsite, yet effectively remove material during the operation. In addition,cutter structures must effectively remove disease or undesired materialwithout damaging delicate neighboring tissue, such as blood vessel wallsor other healthy tissue, which often surrounds and may be attached tothe undesired material. Thus, it is important for cutter structures ofinterventional catheters to accurately and reliably differentiatebetween the diseased or undesired material and healthy tissue.

Differential cutting blades exert high shear forces against relativelyhard substrates to cut or ablate relatively hard, inelastic, material.Softer, elastic structures, such as healthy tissue, blood vessel wallsand the like, are deformed and displaced rather than cut by differentialcutting blades, thereby reducing the shear forces and protecting elasticstructures from damage. Less elastic material does not deform whencontacted by a differential cutting blade, and shear stresses areconsequently exerted on less elastic material to cut or scrape thematerial without damaging elastic tissue in proximity. In this manner,fragments of diseased, undesirable material are removed by differentialcutting blades, while the more elastic, healthy tissue remainsundamaged.

U.S. Pat. No. 4,445,509 describes differential cutting in the context ofan atherectomy device. This patent describes a cutter assembly having aplurality of cutting flutes, each cutting flute having a blade surfaceoperating according to the principle of differential cutting. Aspirationports are provided in the body of the cutter assembly for collection andremoval of particulates and liquids from the site of the intervention.U.S. Patent Publication 2004/0006358 A1 also discloses differentialcutting surfaces forming an acute angle of attack with respect to theocclusive material. Aspiration ports are provided between the cuttingsurfaces.

Some interventional catheters use diamond grit on a cutting surface inan effort to provide highly divided, small particle size debris. Diamondgrit particles, however, do not operate as differential cutters exceptin their smallest embodiment because, depending on their orientation onthe cutting surface, their exposed surfaces form random cant anglesproducing different cutting characteristics at different points ofcontact with tissue. Relatively coarse diamond grit can act as adifferential cutter because of the ratios of diamond size and populationto tissue flexibility, but typically is more likely to damage elastic,healthy tissue such as blood vessel walls. Relatively fine diamond grithas slow material removal rates, requiring the use of higher rotationalspeeds. The use of grit or abrasive particles or surfaces is, however,beneficial in many applications.

The extent and consistency of the disease or undesired material formingan obstruction are frequently not well characterized prior to theintervention. Thus, although interventional catheters and cutterassemblies having different sizes and material removal properties may beprovided, and may even be interchangeable on a material removal system,it is difficult to ascertain which combination of features will be mosteffective in any particular intervention prior to insertion of thedevice. Various quick-connect systems have been developed to permitremoval and installation of multiple operating catheters during a singlesurgical intervention. Interchange, withdrawal and insertion of multipleinterventional catheters, however, is time consuming, and may result inincreased blood loss and increased risk to the patient.

Providing access to multiple cutter assemblies having different sizesand different material removal properties on a single interventionaloperating catheter is highly desirable. Interventional catheters havingcutter or material removal assemblies that can be operated to vary thesize of the cutting profile at the material removal site are known.Cutter assemblies comprising a distal cutter assembly having fixedblades and a proximal cutter assembly having pivoting blades aredescribed, for example, in U.S. Pat. Nos. 6,565,588 and 6,818,001.

Several prior art interventional catheters provide for aspiration ofliquids and/or debris from the material removal site. Numerousinterventional catheters also provide infusion of a liquid to the siteof the intervention. Infused liquids may assist in the material removalprocess, or may be used to deliver diagnostic, imaging or therapeuticmaterials prior to, during or following an intervention.

Although interventional catheters are used frequently, limitations inthe flexibility, reliability and versatility, together with capabilityof use and performance of existing systems limit the types of diseaseconditions that can be effectively treated. There thus remains a needfor improved interventional catheter assemblies.

SUMMARY OF INVENTION

The present invention provides interventional catheters that may beemployed to rapidly and effectively remove unwanted material from bodylumens or cavities. Interventional catheters and control systemsdisclosed herein may be adapted for use within a variety of body lumensor cavities such as blood vessels and vascular cavities,gastrointestinal cavities, lumens or cavities in the urinary system andin male and female reproductive organs, and other fluid cavities such aspulmonary lumens and gas exchange cavities, nasal and sinus cavities,and the like. The lumen or cavity may form a generally tubularstructure, such as a blood vessel, a ureter, a fallopian tube, a nasalpassageway, and other tubular passageways. For example, systems of thepresent invention may be used for removing undesired material fromnative blood vessels such as native coronary, renal, cranial, peripheraland other blood vessels, artificial or grafted vessels such as saphenousvein grafts, and the like. The lumen may have implanted devices such asstents in place. The lumen or cavity may be within, or in proximity to,an organ such as a kidney, gall bladder, lung or the like, or the bodycavity may form part of another system, such as a lymph node, spinalcanal, or the like. Interventional catheters are generally used toremove unwanted material from a target site in body lumens or cavitiesof mammalian subjects, particularly human patients.

The undesired material that is removed using interventional catheterassemblies and control systems disclosed herein may be disease materialsuch as atherosclerotic plaque, calcified plaque, thrombus, or othertypes of deposits, gallstones, a valve or portion thereof, and the like.In certain embodiments, the interventional catheter assemblies disclosedherein are employed in the treatment of cardiovascular or peripheralartery disease (PAD) to remove disease material from blood vessels,including peripheral blood vessels.

The present interventional catheter assembly includes a catheter systemthat is at least partially inserted and navigated within a patient'sbody while an operator controls the system externally of the cathetersystem. The interventional catheters disclosed herein incorporate amaterial removal component, referred to herein as an “operating head,”which is generally positioned at or near the distal end of theinterventional catheter system. As used herein, “proximal” refers to adirection toward the system controls and the operator along the path ofthe catheter system, and “distal” refers to the direction away from thesystem controls and the operator along the path of the catheter systemtoward or beyond a terminal end of the operating head.

Fluidic communication between the operating head and externallypositioned components of the interventional catheter system is generallyprovided by one or more sealed passageways of the catheter system. Othertypes of communication systems or pathways may also be provided fordelivery of power, for rotationally driving and translating theoperating head, for implementing various control features, and the like.The operating head may be driven, or controlled, using electricalsystems, radio frequency and other remote control systems, mechanicalsystems, magnetic systems and other systems or modalities suitable forremote operation of an operating head. The operating head may alsoincorporate features providing additional functionalities such asultrasound guidance, various types of imaging features, and the like.The system components described below are described as exemplarycomponents and are not intended to limit the scope of the invention.

The interventional catheter system may be used in conjunction with aflexible guidewire that is navigated through internal pathways, such asblood vessels, to a target material removal site. For partialobstructions, the guidewire is generally placed across the lesion andthe operating head of the interventional catheter is advanced on theguidewire to the target site and then into and through the lesion. Whena lumen is totally obstructed and a guidewire cannot penetrate theobstruction without causing harm to nearby tissue or riskingembolization, the operating head may be advanced beyond the distal tipof the guidewire and into and through the obstruction, or the operatinghead and guidewire may be advanced in tandem. Other methods that may beemployed for guiding and steering the operating head include, but arenot limited to, radio frequency systems, stereotactic systems, magneticsystems, remote control systems, and the like. The interventionalcatheters disclosed herein may be adapted for use with any of thesesteering systems.

The operating head is rotatable, incorporates cutter elements, and isoperably connected to a rotatable and axially translatable drive shaft,drive system and control systems. In preferred embodiments, theoperating head comprises at least one blade having a cutting surfacethat operates according to the principles of differential cutting.Although the “cutting” surfaces or blades of an interventional catheterof the present invention may be sharp and may actually “cut” material atthe target site, the term “cut” or “cutting” or “cutter” or “blade(s),”as used herein, refers to cutting, scraping, abrading, ablating,macerating and otherwise breaking down undesired material into particlesor smaller, removable, units of material. Cutter assemblies disclosedherein generally comprise a plurality of differential cutting blades andmay incorporate fixed and/or adjustable blades as disclosed, forexample, in U.S. Pat. Nos. 6,565,588 and 6,818,001, which areincorporated herein by reference in their entireties. Differentialcutting blades are also disclosed, for example, in U.S. PatentPublication 2004/0006358 A1, which is incorporated herein by referencein its entirety. In some embodiments, the operating head may comprise anabrasive surface or an abrasive material provided on a surface of arotational element.

In one embodiment, interventional catheters have an operating headincorporating a cutter assembly having a plurality of radially arranged,fixed blades, each blade providing a differential cutting surface at aleading edge. The term “leading” edge or surface, as used herein,indicates the edge or surface that contacts material during rotation ofthe operating head in a direction to achieve removal of material bycontact with the edge or surface, and the term “trailing” edge orsurface, as used herein, indicates the edge or surface generally“behind” or on an opposite side of the leading edge. In one embodiment,a fixed blade cutter assembly comprises a plurality of raised cuttingsurfaces having depressions between adjacent cutting surfaces, with boththe blade and depression structures terminating in a generally smoothdistal collar.

Cutter assemblies may optionally incorporate openings or ports providingaccess to an internal cavity communicating, for example, with a sealedlumen of the catheter for aspiration and/or infusion of fluids. Portsmay be provided in a fixed blade or adjustable blade cutter assembly, orboth. In a fixed blade cutter assembly, ports may be located between allor a portion of the cutting surfaces and are preferably provided in aradially symmetrical arrangement in a generally proximal portion of thecutter assembly. In alternative cutter assemblies, there are no ports oropenings providing access to the interior of the cutter assembly.

The cutter assembly may comprise one or more cutters or cutting surfacesand one or more distinct types of cutter elements. For example, a dualcutter configuration incorporates a fixed diameter cutter and anadjustable diameter cutter in combination. Dual cutter assemblyconfigurations are described in the prior art publications incorporatedherein by reference and may present two different material removalprofiles in two different operational modes. In one mode, the cutterassembly is rotated and advanced to remove occlusive material in aninitial “pilot pass” in which the fixed diameter cutter is the primarycutter, and the adjustable diameter cutter is in a smaller diametercondition. Following one or more pilot passes, the adjustable diametercutter may be adjusted to a larger diameter condition in a second modeof operation, and the dual cutter assembly may be advanced so that theadjustable diameter cutter, in its expanded condition, operates as theprimary cutter and clears an even larger volume of occlusive material.Following this material removal operation, the adjustable diametercutter may be adjusted to a smaller diameter condition and the dualcutter assembly may be withdrawn from the site. This method, using thematerial removal system of the present invention, obviates the need forthe operator to remove and replace, or interchange, cutter assembliesduring a material removal operation to provide cutters having differentdiameters and material removal capabilities.

According to one embodiment, fixed blade cutter assemblies of thepresent invention incorporate differential cutting surfaces having aleading edge cant angle of less than 90°, and preferably incorporatedifferential cutting surfaces having a leading edge cant angle of lessthan 80°. The trailing edge cant angle may be different from the leadingedge cant angle, and is generally less than the leading edge cant angle.Fixed blade cutter assemblies may incorporate differential cuttingsurfaces having generally planar leading and trailing faces. In oneembodiment, the generally planar differential cutting surfaces arecontinuous and generally smooth, and they do not provide anycommunication with internal spaces of the cutter assembly. In general,any number of blades, generally from about three to about twelve, may beprovided in a radially symmetrical arrangement. In one illustrativeembodiment, ten fixed cutter blades are provided in a cutter assemblyhaving multiple ports providing access to an internal cavity. In anotherillustrative embodiment, four fixed cutter blades having smooth,continuous surfaces with no openings are provided.

Interventional catheters of the present invention incorporating a fixedblade cutter assembly may additionally comprise cutter blades presentingdifferential cutting surfaces having a different configuration, profileand/or cant angle. Additional cutter surfaces may be provided proximallyto the fixed blade cutter assembly, for example, as adjustable (e.g.,pivoting) cutting blades, as described in the patent publicationsincorporated herein by reference. Pivoting cutting blades may be mountedfor limited rotation on a rotating structure with or without ports thatcommunicate with an internal space for aspiration and/or infusion. Ingeneral, any number of blades, generally from about three to abouttwelve, may be provided in a radially symmetrical arrangement. Accordingto one embodiment, adjustable blade cutter assemblies of the presentinvention may incorporate differential cutting surfaces having a leadingedge cant angle of less than 100° and greater than 80°.

Cutter assemblies comprising an operating head having a combination ofcutter blades and another material removal modality are alsocontemplated. In some embodiments, fixed or adjustable cutting bladesmay be provided in an operating head in combination with a non-cuttingmaterial removal system, such as a laser-based device, a high frequencyultrasound device, or a heating and/or electrically ablative device. Thefixed or adjustable cutting blades may be positioned proximal to ordistal to the non-cutting material removal system.

Cutter assemblies incorporating cutter surfaces having a steppedconfiguration are disclosed herein and are preferred for manyapplications. Stepped blades have a raised cutting surface or bladepositioned adjacent a shoulder portion that is generally atraumatic totissue. This blade configuration essentially limits the depth of tissuecut during rotation of the blade to the depth of the raised cuttingsurface. Both fixed and adjustable cutting blades may be provided withstepped cutting surfaces. More aggressive or less aggressive blades maybe designed and provided, depending on the dimensions of the raisedcutting surface, the cant angle of the cutting edge of the raisedcutting surface, and the relative dimensions of the raised cuttingsurface, the width of the shoulder portion and other blade surfacegeometries. Suitable stepped cutter blade geometries may incorporate aleading edge cant angle of greater than 70°, more preferably greaterthen 80°, and in some embodiments between about 80° and 110°. Theseblades present a more aggressive leading cutting edge than blades havinga lower cant angle, but they demonstrate a reduced and generally morebenign cutting profile because the effective cutting edge is limited bythe configuration of the cutting edge and the presence of the generallyatraumatic shoulder portion.

In certain embodiments, the interventional catheters disclosed hereininclude an aspiration system for removal of debris from the interventionsite via aspiration through one or more aspiration ports. Aspirationsystems suitable for use in interventional catheters of the presentinvention are described, for example, in the patents incorporated hereinby reference and in U.S. Patent Publication 2004/0220519 A1, which isalso incorporated herein by reference in its entirety. Debris generatedduring a material removal operation is entrained in fluids (e.g. blood),and the aspirate fluid containing debris is removed by aspirationthrough material removal port(s) provided in proximity to the cutterassembly and withdrawn through a sealed lumen of the interventionalcatheter. The sealed lumen is connectable to an aspirate collectionsystem.

Liquid infusion may be provided in, or in proximity to, the operatinghead. Infusion of liquids may be used to provide additional liquidvolume for removal of debris, or to deliver lubricating fluids,treatment agents, contrast agents and the like. Infusion of fluids suchas saline in proximity to the target material removal area may bedesirable because it tends to reduce the viscosity of the materialsbeing removed, thus facilitating removal through relatively smalldiameter lumens. Liquid infusion may be provided distal or proximal tothe operating head, and/or may be provided through the operating head.Liquid infusion systems are well known in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an interventional catheter assemblycomprising an operating head mounted at or near a distal end of acatheter system, a controller and a console unit.

FIG. 2A is an enlarged perspective view of one embodiment of a fixedblade distal cutter assembly of the present invention.

FIG. 2B is a cross-sectional view, illustrating the leading edge cuttersurface cant angles for the differential cutter blades of the cutterassembly of FIG. 2A.

FIG. 3 is an enlarged perspective view of a dual cutter assembly of thepresent invention having a distal fixed blade assembly and a proximaladjustable blade assembly.

FIG. 4 is an enlarged perspective view of the fixed blade cutterassembly illustrated in FIG. 3.

FIG. 5A is an enlarged perspective view of a stepped cutter blade of thepresent invention.

FIG. 5B is an enlarged cross-sectional view of the stepped blade of FIG.5A taken through line 5B-5B.

FIG. 6 is an enlarged schematic end view of a cutter assemblyincorporating a distal fixed blade cutter assembly as shown in FIG. 4and an adjustable blade cutter assembly employing stepped cutter bladesas illustrated in FIGS. 5A and 5B.

FIG. 7 is an enlarged perspective view of another stepped bladeconfiguration of the present invention.

DETAILED DESCRIPTION

Certain preferred embodiments are described herein with reference to amaterial removal device having a rotational cutting head. It will beappreciated that this device embodiment is being described asillustrative and that the inventions and features disclosed herein areapplicable to interventional catheters having different types ofoperating heads.

FIG. 1 illustrates an exemplary embodiment of an interventional catheterassembly 10 comprising console unit 12, controller 30, and cathetersystem 32 having a rotatable operating head 40 located at or inproximity to the distal end of the catheter system and incorporating oneor more cutter assemblies. Controller 30 may be used to manipulate (e.g.advance and/or rotate) the catheter system 32 and operating head 40, oralternative controls may be provided. The configuration of the operatinghead and cutter assemblies will be described below with reference toFIGS. 2-7.

Console unit 12 may incorporate an infusion pump 14 and/or an aspirationpump 16. During operation of the interventional catheter, an infusateconduit 18 draws fluid from an infusate reservoir 20 and operablycontacts the infusion pump 14 to provide fluid through an infusion lumenin catheter system 32 to one or more infusion ports provided inproximity to the operating head. Similarly, but in reverse, fluids withentrained particulates may be withdrawn from the site of interventionthrough an aspiration lumen in catheter system 32 and conveyed toaspiration conduit 22, which is in operable contact with the aspirationpump 16, and communicates with the aspirate collection vessel 24.Console unit 12 may also provide a power source for operating theoperating head and system components, or it may be in communication withan external power source. In the illustrated embodiment, console unit 12provides power to the interventional catheter assembly and controller 30by means of a device power port 25 and power cord 26.

Various microprocessor, electronic components, software and firmwarecomponents may be provided within or in communication with the consoleunit for controlling operation of the interventional catheter asdescribed herein. Software may be provided in a machine-readable mediumstoring executable code and/or other data to provide one or acombination of mechanisms to process user-specific data. Alternatively,various systems and components may be controlled using hardware orfirmware implementations. Data storage and processing systems may alsobe provided in console unit 12.

One function of console unit 12 is to provide feedback of system and/orenvironmental conditions or operating parameters. The console unit mayoutput operational information concerning operating conditions andfeedback from the material removal site to the operator. According toone embodiment, console unit 12 provides continuously updated output toan operator of operating parameters such as operating head rotationrate, which may include the actual run speed as well as the desiredspeed; operating head advance rate; aspiration rate and/or volume;infusion rate and/or volume; elapsed run-time; and the like.

Certain automated and selectable control features may be implemented inconsole unit 12. Preset routines or programs involving various operatingparameters may be preselected, stored and selectable by an operator, forexample. Thus, according to one embodiment, the disclosed materialremoval system implements control features based on an operator's inputof specified parameters. Specified parameters may include, for example:lesion length, lesion type and character, such as calcified, fibrotic,lipid/fatty and the like; historical factors, such as restenosis; rateof blood flow; volume of blood flow; percentage of restriction; lumentype and/or location; lumen diameter; desired rotation rate and/orrotation profile for the cutter assembly; desired advance rate and/oradvance profile for the cutter assembly; desired aspiration rate and/orprofile; desired infusion rate and/or profile; and the like. Based onthe specified parameters input by the operator, the control unit maycalculate and implement automated operating conditions, such as: cutterassembly rotation rate and profile; cutter assembly advance rate andprofile; aspiration rate and profile; infusion rate and profile; cutterassembly size; and the like. Various system operating parameters,operating conditions, patient conditions, and the like may also berecorded and stored during interventions to preserve a record of thepatient and intervention operational parameters.

In one embodiment, console unit 12, together with aspiration pump 16 andinfusion pump 14 and the associated control and display features, isprovided as a separate, re-usable unit, that may be used as standardequipment in operating rooms, for example. In the system illustrated,console unit 12 is not contaminated by contact with blood or aspirateduring operation, and the power and control systems are durable andlong-lasting and may be reused for many interventions. Console unit 12may be provided in a housing designed to sit on a platform duringoperation, or the housing may be designed for mounting on a portablestructure, such as an i.v. pole or another structure. The interventionalcatheter system, comprising the catheter system 32 with operating head40, controller 30, aspirate conduit 22, aspirate collection vessel 24,and infusion conduit 18 may be provided as a sterile, single use systemkit.

The catheter system and operating head are described below withreference to a rotatable operating head employing a cutter assemblyhaving a plurality of cutter blades for material removal. Ininterventional catheter applications incorporating aspiration and/orinfusion systems, aspiration and/or infusion conduits terminate at orwithin controller 30, where they communicate with aspiration andinfusion lumens within the catheter system 32. A rotatable drive shaftfor driving the operating head is provided in catheter system 32. Aguidewire may also transit controller 30 and catheter system 32. Ingeneral, controller 30 or an associated control mechanism providesuser-operated mechanisms for rotating and/or translating the operatinghead. Controller 30, which is constructed from a durable, sterilizablematerial, such as hard plastic, may be provided in any convenientergonomic design and constructed for placement in proximity to and/or incontact with the external body. In one embodiment, the controller mayinclude an integrated handle for operator convenience in holding andsupporting the controller during operation. Catheter system 32, exitingcontroller 30, is axially translatable with respect to controller 30 asthe operating head and catheter system are guided to a target materialremoval site. It will be appreciated that some of the control andoperational features described herein with reference to controller 30may be provided in console unit 12 and, likewise, some of the controland operational features described with reference to console unit 12 maybe provided in controller 30.

The operating head 40 of the interventional catheter disclosed hereinmay comprise any of a variety of rotational cutting devices orassemblies having one or more cutting surface(s) for cutting,fragmentizing, pulverizing, ablating, scraping, grinding or otherwisereducing the size of undesired material and/or separating undesiredmaterial from healthy tissue, such as the walls of a blood vessel, inproximity to the target removal site. Differential cutter assemblies maybe provided, as described in the U.S. patent publications incorporatedherein by reference. Operating heads comprising abrasive rotationalsurfaces may also be used. The operating head, or sub-componentsthereof, such as the cutting surfaces, may be coated with a radio-opaquematerial such as gold, platinum, inks and the like, to render theoperating head radioscopically visible and to assist a medicalprofessional in guiding and positioning the cutter assembly relative toan occlusion.

Exemplary materials for construction of the cutting surface(s) of cutterassemblies of the present invention include metals, metal alloys,ceramics and cermet materials such as, but not limited to, various typesof stainless steels, such as series 300 and/or 400, vanadium steel,nickel-titanium, titanium, titanium-containing metals and oxideceramics. Metallic materials such as stainless steels may be hardenedusing well-known techniques. In general, cutter surfaces are constructedfrom hard materials and may be treated to impart even greater hardnessto the cutter surfaces.

FIG. 2A illustrates a fixed blade cutter assembly having a plurality ofdifferential cutting surfaces according to the present invention. Cutterassembly 40 comprises a plurality of cutter blades 42 arranged in aradially symmetrical arrangement with respect to a central longitudinalaxis of the cutter assembly. Each of the cutter blades 42 is joined at adistal end to form a distal bore 44 which serves as a rotating bearingfor a guidewire 45. In cutter assemblies that are employed withoutguidance over a guidewire, cutter blades 42 may alternatively terminateat their distal ends in a blunt or rounded or pointed structure withoutforming a distal bore. Cutter blades 42 terminate at their proximal endsin a proximal ring-like collar 46.

In various types of interventional catheters, cutter assembly 40 may bemounted to a drive shaft, a catheter system, or an intermediate bearingstructure. FIG. 2 illustrates an embodiment in which cutter assembly 40is mounted to a rotating element 52 of bearing 50. A non-rotatingelement 54 of the bearing is mounted to a distal portion of catheter 56or another cylindrical structure provided at a distal portion of theinterventional catheter. The rotating bearing element and cutterassembly are rotated during operation by the drive shaft, while thenon-rotating element of the bearing structure and the distal portion ofthe catheter remain stationary during rotation of the operating head.

The overall outer configuration of cutter assembly 40 is generally roundfrom an axial view and oblong or frusto-conical from a profile view. Theouter edges of cutter blades 42 taper along a curved line betweensmaller diameter distal bore 44 and larger diameter proximal collar 46,such that the diameter of the cutter assembly decreases toward itsdistal end. This configuration allows the smaller diameter distal end ofthe cutter assembly to penetrate an obstruction or partial obstructionwhile providing a progressively larger bore as the cutter assembly isadvanced through the obstruction.

Each of the cutter blades 42 has a differential cutter surface on aleading edge 43 that contacts material to be removed when cutterassembly 40 is rotated during a material removal operation. Differentialcutter surfaces may be optimized for use in different types of cuttingenvironments, for different types of materials being removed, and fordifferent applications, by providing different cant angles. In general,the higher the cant angle the more aggressive the action of the cuttersurface. A cutter surface having a cant angle of less than 90° haspreviously been shown to be gentle and benign when it contacts aresilient surface, such as the wall of a body lumen, yet it effectivelycuts and abrades less resilient materials, such as plaque, calcifiedmaterial and thrombus, to provide effective removal of disease material.Cutter assemblies disclosed herein are benign to healthy, elastic tissuewhile providing effective removal of less elastic, disease tissue.

The leading edge cutter surfaces are preferably generally smooth,although they may be provided as abrasive surfaces, or surfaces coatedwith abrasive materials, in alternative embodiments. The use of diamondgrit or other types of abrasives on the cutting surfaces may reduce thesize of particles generated during rotation of cutter assemblies,thereby improving the efficiency of removal of the particles andreducing the risk of undesirable side effects. The use of diamond gritor other types of abrasives is particularly advantageous when removinghard materials, and/or small, targeted areas of unwanted material. Thediamond grit or other type of abrasive employed on the cutting surfacesmay have a particle size of about 400 microns or less. In someembodiments, the abrasive materials have a particle size of about 100microns or less, while in some embodiments, the abrasives have aparticle size of about 40 microns or less, generally between about 20and 40 microns in size.

The cant angle α formed by the leading edges 43 of cutter blades 42 anda line tangent to a circle circumscribing the outer edges of the cuttersurfaces are illustrated in FIG. 2B. Cant angles α formed by leadingedges 43 of cutter surfaces 42 are preferably less than 90°. In someembodiments of fixed blade cutter surfaces disclosed herein, the cantangle of the cutter blades is less than 80° and, in some embodiments, isabout 70°. Trailing angles β formed by trailing edges 45 of cuttersurfaces 42 are preferably less than the corresponding cant angles and,in many embodiments, are less than 70°.

The number of cutter blades provided on a fixed cutter assembly of thepresent invention may vary depending on the interventional applicationand the nature of the material being removed. As few as three blades maybe provided and as many as 12-15 blades may be provided in a radiallysymmetrical arrangement. Fixed blade cutter assemblies having 7 or moreblades are preferred for many applications. In one embodiment, asillustrated in FIG. 2A, a plurality of generally oval ports 48 may beprovided between neighboring blades for communication with an internalspace of the cutter assembly. Ports 48 may be provided between each pairof neighboring blades, as illustrated, or fewer ports may be provided.In one embodiment, as illustrated, ports 48 are preferably provided in aproximal portion of the cutter assembly in proximity to the proximalcollar. Ports 48 may be used as aspiration or infusion ports andcommunicate with an appropriate aspiration or infusion lumen providedwithin catheter 56. Additional aspiration and/or infusion ports may beprovided in locations proximal to the cutter assembly.

FIG. 3 illustrates another cutter assembly for interventional cathetersof the present invention in which a dual cutter assembly 60 comprises afixed blade cutter 70 and an adjustable blade cutter assembly 80. Invarious types of interventional catheters, cutter assembly 60 may bemounted to a drive shaft, a catheter system, or an intermediate bearingstructure. FIG. 3 illustrates an embodiment in which cutter assembly 60is mounted to a rotating element 92 of bearing 90. A non-rotatingelement 94 of the bearing is mounted to a distal portion of catheter 96or another cylindrical structure provided at a distal portion of theinterventional catheter. The rotating bearing element 92 and cutterassembly 60 are rotated during operation by the drive shaft, while thenon-rotating element of the bearing structure 94 and the distal portionof the catheter 96 remain stationary during rotation of the operatinghead.

Fixed blade cutter assembly 70, illustrated in isolation in FIG. 4,comprises a plurality of differential cutting surfaces 72. The overallouter configuration of cutter assembly 70 is generally round from anaxial view and oblong or frusto-conical from a profile view. The outeredges of cutter blades 72 taper along a curved line between smallerdiameter distal bore 74 and larger diameter proximal collar 76, suchthat the diameter of the cutter assembly decreases toward its distalend. This configuration allows the smaller diameter distal end of thecutter assembly to penetrate an obstruction or partial obstruction whileproviding a progressively larger bore as the cutter assembly is advancedthrough the obstruction.

Each of the cutter blades 72 is fixed on the cutter assembly andpreferably has a differential cutter surface on a leading edge 73 thatcontacts material to be removed when cutter assembly 70 is rotatedduring a material removal operation. The leading edge cutter surfacesare preferably generally smooth, although they may be provided asabrasive surfaces, or surfaces coated with abrasive materials, inalternative embodiments. The blades may be provided as generally planarsurfaces 75 at a distal portion, terminating proximally in a curved orscooped area 77. The cant angles formed as described above by theleading edges 73 of cutter surfaces 72 and a line tangent to a circlecircumscribing the outer edges of the cutter surfaces at each cuttersurface are preferably less than 90°. In some embodiments of fixed bladecutter surfaces disclosed herein, the cant angle of the cutter blades isless than 80° and, in some embodiments, is about 70°. The trailingangles β formed by the trailing edges 78 of cutter surfaces 72 and aline tangent to a circle circumscribing the edges of the cutter surfacesare generally less than the cant angle α and, in many embodiments, areless than 70°.

The fixed blade cutter assembly 70 does not have ports or openings,other than the guidewire bore 74, communicating with an interior of theassembly. Aspiration and/or infusion ports may be provided elsewhere inproximity to the cutter assembly, if desired. The number of cutterblades provided on fixed cutter assembly 70 of the present invention mayvary depending on the interventional application and the nature of thematerial being removed. As few as three blades may be provided and asmany as 5-7 blades may be provided in a radially symmetricalarrangement. Fixed blade cutter assemblies having 3 or more blades arepreferred for many applications.

Cutter assembly 60 illustrated in FIG. 3 also incorporates an adjustableblade cutter assembly 80 having a plurality of cutter surfaces 82presenting a different cutting profile than that of cutter surfaces ofthe distal blades 72. Many different types of adjustable blade cutterassemblies are known in the art and may be used in combination with afixed blade distal cutter assembly of the present invention. Cutterassembly 80 may comprise a plurality of pivoting blades, for example,that move between a tangential, non-cutting, position and a radial,cutting, position by changing the direction of rotation of the cutterassembly. The fixed blade cutter assembly may be operated in onedirection of rotation in a first cutting operation to clear apassageway, and the adjustable blade cutter may be operated in anopposite direction of rotation in a second cutting operation to clear alarger opening in a lumen or cavity. Cutter assemblies of this type aredescribed in the patent publications incorporated herein by reference.

FIGS. 5A and 5B illustrate a stepped cutter blade configuration that maybe incorporated in cutter assemblies of the present invention. Whilecutter blade 93 is illustrated as a generally fan-shaped, flat bladesuitable for use, for example, in an adjustable blade cutter assembly,it will be appreciated that the stepped blade cutter configuration maybe incorporated in cutter blades having a variety of configurations,including fixed cutter blades and different configurations of adjustablecutter blades. Cutter blade 93 illustrated in FIGS. 5A and 5B isdesigned to rotate in a clockwise direction A. Cutter blade 93 has aleading edge cutting surface 99 adjacent or in proximity to a shoulderregion 97 and a trailing surface 98. An angled or chamfered surface 95may be provided between shoulder region 97 and the leading surface 91 ofthe cutter blade. As cutter blade 93 rotates in clockwise direction A,the leading surface 91 or chamfered edge 95 of blade 93 contacts thetissue first, followed by the shoulder 97 and cutter surface 99. Theleading surface 91, chamfered edge 95 and shoulder 97 are generallyatraumatic to tissue, while cutter surface 99 exerts a material removalaction. Cutter surface 99 preferably forms a cant angle α of from about60° to about 110°, more preferably from about 70° to about 100°, andmore preferably yet from about 80° to about 95°, with respect to a lineT tangent to the circumscribed arc of the circumference of the cutterassembly.

The height “X” of the cutter surface 99 from its outer edge to the pointwhere it joins shoulder 97 is one factor that governs the“aggressiveness” of the cutter blade. For a given cant angle α, ashorter cutter surface X removes generally less material per pass than alonger cutter surface X. For many atherectomy and thrombectomyapplications, cutter surface X may have a height X of from about 0.0005to 0.010 inch, with heights of from about 0.001 to 0.003 inch beingespecially preferred. The height X may be substantially uniform alongthe length of the cutter surface, or it may taper along the length ofthe cutter assembly. In general, the cutter surfaces provided on acutter assembly have the same or a similar cant angle and height X, butwhen multiple cutter assemblies are provided, the cant angles andheights X of cutter blades provided on the different cutter assembliesmay be varied to vary the cutting properties of the assemblies.

Shoulder region 97 is provided adjacent or in close proximity to cuttersurface 99 and may have a substantially flat profile, or an angled orcurved profile. The angle “Y” formed by the plane of cutter surface 99and shoulder 97 is preferably from about 45° to about 150°, morepreferably from about 60° to about 120°, and more preferably yet fromabout 80° to about 110°. The width “W” of shoulder region 97 ispreferably greater than the height X of cutter surfaces 99. In oneembodiment, the width W of shoulder region 97 is from about 1.5 to about10.0 times the height X of cutter surface 99; in another embodiment thewidth W of shoulder region 97 is from about 2.0 to about 4.0 times theheight X of cutter surface 99. For atherectomy and thrombectomyapplications, the width W of shoulder 97 is preferably from about 0.001to about 0.015 inch, and the width W of shoulder 97 is more preferablyfrom about 0.003 to about 0.010 inch.

Optional chamfered surface 95 may be provided as an angled or curvedsurface between the leading blade surface 91 and shoulder 97. Chamferedsurface 95 is generally narrower than shoulder 97 and may have aconstant width over its length, or it may taper from one end to another,or toward and away from a central blade portion. Chamfered surface 95and shoulder 97 contact and displace the surface of tissue prior tocontact between the tissue surface and the cutting surface 99, therebyrestricting the depth of the “bite” that cutter surface 99 takes in thetissue and reducing the risk of damage to tissue. The protective effectof chamfered surface 95 and shoulder 97 enables the use of cuttingsurfaces having more aggressive cant angles, for example cant angles ofabout or greater than 80°, in order to effectively cut hardened diseasematerial, while providing protection to healthy elastic tissue.

Cutter blades 93 may additionally be provided with cut-outs or cavitiesthat penetrate their surfaces in locations that are radially inward ofthe cutter surfaces and shoulders. In one embodiment, a curved slothaving a curve that substantially matches the outer edge of the cuttersurface may be provided, for example, to reduce drag produced byrotation of the blade against fluids. In another embodiment, multipleslots or openings may be provided through the surface of cutter blades93. In general, the slots or openings represent at least about 5% of thesurface area of the blade surface and more typically represent at leastabout 10% to 15% of the surface area of the blade surface. Slots oropenings provided in the cutter blade surfaces generally represent lessthan about 50% of the blade surface area.

FIG. 6 illustrates an end view of an operating head of the typeillustrated in FIG. 3 having a distal cutter assembly of the typeillustrated in FIG. 4 and a proximal cutter assembly having steppedblades of the type illustrated in FIGS. 5A and 5B. The fixed andadjustable blade cutter assemblies provide different cutting profilesand operate in opposite directions of rotation of the operating head.The distal fixed cutter 70 operates as the primary cutter assembly whenthe operating head is rotated in clockwise direction A. Leading bladesurfaces 73 provided at the edges of leading blade faces 75 do not havea stepped configuration and preferably have cant angles α of less thanabout 80°, generally from about 65° to about 90°. Trailing bladesurfaces 78 preferably have cant angles of less than that of the leadingblade faces. Proximal cutter assembly surfaces 77 preferably have acurved or scooped configuration, which is not apparent from the figure.

Proximal blades 93 have a stepped cutter surface configuration andoperate as the primary cutters when operating head 60 is rotated incounterclockwise direction B. Stepped cutter blades 93 present a cuttersurface 99 adjacent shoulder 97, and chamfered edge 95 is presented as aleading surface. When the operating head of FIG. 6 is rotated incounterclockwise direction B, tissue is contacted first by chamferededge 95 (and, to some degree, the leading blade surface positionedradially inwardly from chamfered edge 95) and shoulder 97, which presentsubstantially atraumatic surfaces, and stepped cutter surfaces 99operate as the primary cutter surfaces. Cutter blades 93 preferablyassume a general tangential orientation when the operating head isrotated in clockwise direction A, as disclosed in the patentpublications incorporated herein by reference.

Stepped cutter blades of the present invention may be provided on avariety of fixed and adjustable cutter blades, and on fixed andadjustable cutter assemblies. An enlarged view of a fixed blade cutterassembly similar to that described with reference to the cutter assemblyof FIG. 4 is shown in FIG. 7. In this embodiment, cutter assembly 100has a plurality of cutter blades 102 oriented for operation by rotationin a counterclockwise direction B. Cutter blades 102 incorporateupstanding cutter surfaces 106 adjacent shoulders 104. The embodimentillustrated in FIG. 7 does not incorporate a chamfered edge, but theshoulders 104 provide generally atraumatic contact with tissue. Thetrailing edges of cutter blades 102 may be provided at a shallow angleto cutter surfaces 106, providing a relatively blunt circumferentialedge on cutter blades 102.

It will be recognized that the operating heads, cutter assemblies anddifferential cutting surfaces disclosed herein may be incorporated ininterventional catheters having different types of power, display andcontrol systems, from those described herein. The differential cuttingsurfaces disclosed herein may be incorporated in any type ofinterventional catheter that may be employed for removal of undesiredmaterial located within a human or animal body. While the presentinvention has been described with reference to specific embodiments andfigures, these specific embodiments should not be construed aslimitations on the scope of the invention, but merely as illustrationsof exemplary embodiments. It is further understood that manymodifications, additions and substitutions may be made to the describedinterventional catheter and control system without departing from thescope of the present invention.

We claim:
 1. A medical device for removal of obstructive material from atarget site in a body lumen or cavity comprising an operating headoperably connected to a rotatable drive shaft and positioned inproximity to a distal end of an elongated catheter, the operating headincluding a support and a plurality of cutting blades extending from thesupport and arranged radially around a central axis of the operatinghead, wherein a cross-section of at least one of the blades has astepped blade cutter configuration having a leading edge cutting surfaceadjacent or in proximity to a shoulder region which is adjacent to aleading surface, the shoulder region being positioned between theleading edge cutting surface and the leading surface, wherein theshoulder region has a width that is greater than a height of the leadingedge cutting surface along substantially its entire interface and formsan angle with the plane of the leading edge cutting surface of fromabout 60° to about 120°, and wherein the leading surface and theshoulder region are generally atraumatic to tissue, while the leadingedge cutting surface exerts a material removal action.
 2. The medicaldevice of claim 1, wherein the drive shaft is translatable and driven bya drive motor and received through the elongated catheter.
 3. Themedical device of claim 1, wherein the height of the leading edgecutting surface is 0.0005 inch to 0.010 inch.
 4. The medical device ofclaim 1, wherein the height of the leading edge cutting surface is 0.001inch to 0.003 inch.
 5. The medical device of claim 1, wherein a ratio ofthe width of the shoulder region to the height of the leading edgecutting surface is more than 2:1.
 6. The medical device of claim 1,wherein the stepped blade cutter configuration additionally comprises achamfered edge provided adjacent to an edge of the shoulder regionopposite to the leading edge cutting surface.
 7. The medical device ofclaim 1, wherein the leading edge cutting surface has a cant anglebetween 80° and 110°.
 8. The medical device of claim 1, wherein theleading edge cutting surface and the shoulder region connect to form anangle greater than 90°.
 9. The medical device of claim 1, wherein theleading edge cutting surface has a curved outer profile.
 10. The medicaldevice of claim 9, wherein the leading edge cutting surface has agenerally fan-shaped outer profile.
 11. The medical device of claim 1,wherein the plurality of cutting blades are fixed cutting blades. 12.The medical device of claim 1, wherein the plurality of cutting bladesare adjustable cutting blades.
 13. The medical device of claim 1,wherein at least one of the cutting blades has a cutout that penetratesits surface in a location that is radially inward of the leading edgecutting surface and the shoulder region.
 14. The medical device of claim13, wherein the cut-out is a curved slot having a curve thatsubstantially matches the outer edge of the leading edge cuttingsurface.
 15. The medical device of claim 13, wherein multiple openingsare provided through the surface of at least one of the cutting blades.16. The medical device of claim 1, wherein the leading edge cuttingsurface has a cant angle of less than 90°.
 17. The medical device ofclaim 1, wherein an angle formed by a trailing edge of the at least onecutting blade and a line tangent to a circle circumscribing the edge ofthe leading edge cutting surface is less than 70°.
 18. The medicaldevice of claim 1, additionally comprising a plurality of ports providedbetween at least some of the cutting blades.
 19. The medical device ofclaim 18, wherein the plurality of ports communicate with an infusionlumen or an aspiration lumen.
 20. An interventional catheter assemblyfor removal of obstructive material from a body lumen or cavitycomprising an operating head operably connected to a rotatable,translatable drive shaft, the drive shaft being driven by a drive motorand received through an elongated catheter, wherein the operating headcomprises a support and a plurality of differential cutting bladesextending from the support and arranged radially around a central axisof the operating head, wherein a cross-section of at least one of theblades has a stepped blade cutter configuration having a leading edgecutting surface adjacent or in proximity to a shoulder region which isadjacent to a leading surface, the shoulder region being positionedbetween the leading edge cutting surface and the leading surface,wherein the shoulder region has a width that is greater than a height ofthe leading edge cutting surface along substantially its entireinterface, wherein the leading edge cutting surface, the shoulder regionand the leading surface are configured to be positioned to contacttissue during operation, and wherein the leading surface and theshoulder region are generally atraumatic to tissue, while the leadingedge cutting surface exerts a material removal action.
 21. Theinterventional catheter assembly of claim 20, wherein the operating headadditionally comprises a plurality of aspiration ports provided betweenat least some of the differential cutting blades, and the aspirationports communicate with a scaled lumen that is connected to a vacuumsystem for removal of aspirate fluid and obstructive material.
 22. Theinterventional catheter assembly of claim 20, wherein the height of theleading edge cutting surface is 0.0005 inch to 0.010 inch.
 23. Theinterventional catheter assembly of claim 20, wherein the height of theleading edge cutting surface is 0.001 inch to 0.003 inch.
 24. Theinterventional catheter assembly of claim 20, wherein a ratio of thewidth of the shoulder region to the height of the leading edge cuttingsurface is more than 2:1 and less than 5:1.
 25. The interventionalcatheter assembly of claim 20, wherein the leading edge cutting surfacehas a cant angle of less than 90°.
 26. The interventional catheterassembly of claim 20, wherein an angle formed by a trailing edge of atleast one differential cutting blade and a line tangent to a circlecircumscribing an edge of the leading edge cutter surface is less than70°.
 27. The interventional catheter assembly of claim 20, additionallycomprising a plurality of infusion ports provided between at least someof the differential cutting blades, wherein the infusion portscommunicate with an infusion lumen.